The present invention relates to a device for determining a concentration-related quantity of a fluorescent contrast agent applied to an object, in particular a turbid medium, said device comprising a source of electromagnetic radiation for irradiating the object at an excitation wavelength and at least one first detecting means for detecting fluorescent electromagnetic radiation emitted by the contrast agent at a fluorescence wavelength, said first detecting means producing fluorescence intensity data.
The present invention also relates to a method of determining a concentration-related quantity of a fluorescent contrast agent applied to an object, in particular a turbid medium, said method comprising irradiating the object with electromagnetic radiation at an excitation wavelength and detecting fluorescent electromagnetic radiation emitted by the contrast agent at a fluorescence wavelength, thereby producing fluorescence intensity data.
The present invention further relates to a computer program product for determining a concentration-related quantity of a fluorescent contrast agent applied to an object, in particular a turbid medium, and to an optical imaging system for imaging an object, in particular a turbid medium, by monitoring fluorescent radiation emitted by a fluorescent contrast agent applied to the object.
Optical imaging systems for imaging a turbid medium, in particular optical mammography systems for imaging female breast tissue, generally employ a fluorescent contrast agent which is applied to an object to be imaged, e.g. a female breast. Electromagnetic radiation that is incident on the object penetrates into the object and excites the fluorescent contrast agent comprised therein which in turn produces fluorescent radiation (in the near infrared (NIR) range of the optical spectrum). The fluorescent radiation emerging from the object is detected at several orientations or locations relative to the object.
Generally, the contrast agent will not be distributed evenly within an object to be imaged. For instance, in optical fluorescence mammography the agents are taken up in higher concentrations by a tumour than by surrounding healthy tissue, i.e. the relative contrast between lesion (tumour) and background is established by the physiology of the contrast agent uptake. An absolute concentration of the contrast agent can be varied by changing the dose that is injected into the object (administered to a patient) or by varying the time after injection at which imaging is performed.
The minimum concentration of contrast agent useful for acquiring images is given by the detection sensitivity of the imaging system. However, there exists an upper limit of the concentration which is given by the onset of non-linear behaviour of the fluorescence signal due to self-absorption of radiation by the contrast agent. These non-linearities have to be avoided when performing optical imaging because they have an important impact on the observed contrast between those parts of the object which take up lower concentrations of contrast agents, e.g. healthy tissue, and those object regions which take up higher concentrations of contrast agents, e.g. lesions: in the low concentration regime a lesion appears as a bright spot on a relatively dark background. In the high-concentration regime a lesion appears as a relatively dark spot.